You need to rescale all dimensions then tweak for max performance, as needed.

900Mhz: Increase all dimensions by 2.667
1.2Ghz: Increase all dimensions by 2.00

Yes, ALL dimensions are affected. Material should be stout enough to support the extra mass. By the way, accuracy counts. A tiny insignificant error will reduce performance (and you may not even recognize that it is a bit crippled).

So, build it with precision in mind. The presentation of the project on the RC-CAM web site was such that it helped minimize the possibility of errors.

I completed & tested the GPP antenna. I sized it up for 1050 MHz, halfway between 900 & 1200 MHz. The receiver that I have uses an F connector instead of an SMA connector so I used a PCB mounted F connector.

Unbelievable results! Almost no glitches while flying. The only area that has poor reception is almost directly behind the antenna.

Performance will be even better if you build it for the exact frequency you are using (down to the hundredths of an inch). The losses expected when it is not a accurate match are a bit high, due to resonance issues.

When you have the time your should build it as such. You will get more gain (or more precisely put, you will eliminate the match losses). I would expect another 2 or 3 dB's, which is certainly worth the effort.

I gained access to a frequency counter & discovered that the transmitter is broadcasting on 1150 MHz. I scaled another GGP Antenna to that exact frequency, smaller than the previous one tuned for 1050 MHz.

No real noticeable change from the first one. Still very good line of sight reception as long as the airplane is in front of the antenna.